Andrew D. Booth – Britain’s Other “Fourth Man” - History of Computing: Learning from the Past - page 31

Fig. 4. APE(X)C Computer in 1956
The second digital computer APEXC [SEC was the first] has been completed and
is in use. It has shown the expected speed of about several hundred times as fast as
mechanical methods but has exceeded expectation in its reliability and freedom from
breakdown. An improved model is almost complete and will take its place as soon as
the first is sent to its owners, the British Rayon Research Association. [8]
The Annual Reports are slightly confused with regard to the computers' names. It
is possible the names changed over time. Andrew Booth subsequently refers to the
Rayon Research machine as APE(R)C - R for Rayon - and the later APE(X)C - X for
X-ray - was the Birkbeck crystallographers machine, see Figure 4.
4 Booth Multiplier
If the drum reflected Booth's engineering talent, then the Booth multiplier was a dem-
onstration of his mathematical skill. A key component of any computer design is the
arithmetic unit and to provide fast arithmetic it is necessary to have hardware multi-
plication and division. When Booth visited von Neumann in 1947 he obtained details
of von Neumann's design for both a hardware multiplier and divider. Booth described
them in his interview with Evans as “a beautiful divider” but the multiplier as “an
abortion” [1]. When Booth asked von Neumann why he had not used a similar ap-
proach in his multiplier as in the divider, von Neumann assured him it was a theoreti-
cal impossibility and Booth accepted the great man's opinion. Booth told Evans that
when he was designing the APEC computer he realised that von Neumann was wrong
and Booth recollected how, over tea with his wife in a central London cafe, he